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Save my name, email, and website in this browser for the next time I comment. More stable for clients: when a class's implementation is changed, as long as its function signatures are not changed, a program which uses this class will not be affected. Enhances software reuse: by composition including other object as data member and inheritance build a new class based on a base class , software reuse is greatly strengthened. It is designed to enable the compiler to know what kind of a function it is before a function is called.
It also enables the compiler to find out whether a function is properly called i. You can include the names of the parameters into the function prototype to make it look more clear, but the compiler will ignore the parameters.
A block is just a compound statement which includes declarations. You can create a block anywhere you like — just enclose at least one declaration and one statement with braces. So the character of a block is different from a function: a function is of two-way information hiding, while a block is of one-way only.
Each time you run this program, you get the same sequence. It setups up a corresponding relationship between a specific integer and a user-chosen identifier. Instead of having to remember what an integer represents, the programmer can easily remember the selfexplained alias. For example, a set of integers from 0 to 7 represents color black, blue, green, cyan, red, magenta, brown and white. They are visible in all blocks in all files in the same process.
In files other than the one where the global variable is defined, you have to use keyword extern to tell the compiler: "The following global variable whose name is xxx and whose type is xxx is defined elsewhere, and you have to find out where yourself. But if you define a global variable in a header file, then when more than one files include that header file, multiple copies of the same global variable will be instantiated, and you will have link errors.
So you should normally put the definition of global variables in a source file. Because this approach requires each file which uses those global variables to declare all of them which keyword extern one by one, causing redundant code and is error-prone.
The normal approach is to create a separate header file and put all extern declarations of the global variables in it. Logically this header file should have the same name as the source file, but it can be different as shown in the following example.
Therefore global variables should normally not be constant. When you use a constant global variable, you actually want a symbol or an alias for a constant. Therefore it is clearer to use a define to define this constant. If you want to have a constant global variable, you should put it in the header file Any. Compiler will treat it in the same way as a define. Say ; printf "End of main! If you have to have a global resource like that, create a global reference pointer to the resource, which can be initialized to NULL on the spot, then create and initialize the resource in the program.
To access the global variable from this block, use unary scope resolution operator "::" in front of the identifier. Local variables are by default of automatic storage class. The loading and saving time is shorter than memory. By placing a heavily used variable into the register, the total run time can be reduced. However, the compiler may ignore this suggestion, if there is no register available. Not often used. Before the first time of use, if not specially initialized, all numeric variables are initialized to zero.
Otherwise the variable can not keep the value of last time and therefore has no difference with normal local variables. This kind of scope is mainly used by procedural languages. For OO it is rarely needed. They keep their values throughout the execution of the program, and can be referred by any functions that follows their declarations or definitions in the file.
According to PLP, the use of global variables should be avoided unless there is a special need. Therefore, global variables, function prototypes and function definitions, which are out of any function body, are of file scope. Labels are identifiers followed by a colon, i. They are implementation details that functions hide from one another.
They are local variables declared in a block. The identifiers can be reused elsewhere without ambiguity. There are such kind of problems that the direct solution can not be easily expressed, but the relationship between the problem and its simpler version is explicit.
Thus the problem can be simplified repeatedly reduced to a smaller version, until it reaches the simplest case called "base case", and finally becomes known. In short, recursion keeps producing simpler version of the original problem until the base case is revealed.
From logical point of view, recursion is invalid or impractical: you can not use an unknown solution to solve a problem. Therefore it is simple. Iteration solutions are better than recursion in respect to performance, because recursion produces a series of function calls and copies of variables, thus takes more overhead, which iteration can avoid. Recursion is only good when it can mirror the real-world problem more naturally, thus the program is easier to understand and debug.
This is called "exponent explosion". Try to avoid this situation. If the result of the calculation depends on the order of evaluation of the two operands i. A constant variable or pointer should be initialized when declared. In most cases it is achieved by using of qualifier "const". It is also used to define a local variable that shouldn't be changed.
Any attempt to modify the constant variable will be checked out by compiler before the program is run. Using this principle to properly design software can greatly reduce debugging time and improper side effects, and can make a program easier to modify and maintain. Compared with the function call overhead, the program size reduced by not repeatedly include the block of statements may be trivial. In these cases we put "inline" qualifier in front of the function definition to tell compiler to insert the body of the called function into the calling function to avoid a call.
When the inline function is changed, all functions that call it should be re-compiled. Keyword inline is specially useful for wrapper classes. The copy constructor of the passed object is called to make the copy, requiring extra overhead.
The original values are untouched. This is good for data security, but bad for performance. A reference is not a variable. It is just an alias of a variable. When we talk about a variable, it is actually the address of one memory cell used to hold different values. In machine language we would directly use the address to represent the variable, but in high-level languages identifiers are used to present addresses. Although "b" is created "out of" a, but once created they are equal.
Therefore, when a object is passed by reference, a new alias is created in the called function to refer to the address of that object.
With this alias the called object can do anything directly to the object itself. The calling statement of call-byreference is the same as call-by-value, therefore the programmer may forget that he is calling by reference. When the values of the parameters are the default ones, you can omit the parameters.
It is a system-dependent keystroke combination. This calculation has the same priority as manipulation and division. For example, the result of int with float is float. So do not compare floating-point values for equality. Instead, test whether the absolute value of the difference is less than a specified small value. Using assignment operator can save a bit of compiling and running time.
It is useful when the statement is in a loop which will be run many times. As a complete loop, first the condition is checked, if satisfied, the statement is executed, then the control variable is incremented.
Notice that break can only exit one layer of loop. If the number of initializers are less than the number of the array elements, the remaining elements are automatically initialized to zero. But such kind of expression can only be used in declaration. In such way when you need the change the array size you only need to change one place. Only constant variable can be used as array size. Therefore you can not make the array size dynamic by inputting an integer from keyboard in run time and use it as array size.
Therefore by declaring an array of 3 elements then putting a value into the 4th element, you may have overwritten another variables and produced very serious logic errors which is very difficult to find out. Therefore, the size of an array should be carefully observed. An array such as char buf[80] however, points to a block of memory allocated by the compiler.
If a block of characters ends with NULL i. Because the bytes are constant, you can never amend the content of the string. Therefore, if you want to amend the content of "Hello world! You have to copy the constant bytes into a character array: char str[]; strcpy str, "Hello world!
You can then amend the content of the array later. Because as said before, the array name is a constant pointer which can not be assigned. So it is not a NULL-terminated string and can not be used in string manipulation functions such as strcpy, strlen, strcat, etc. Average comparison time: half of the array size. Binary search: can only be applied on sorted array. By checking the middle element you will find out which half of the array contains the element.
Maximum comparison time: log n arraysize. If an array needs to be searched frequently, then it is worthwhile to spend a great time to sort it first. The first dimension does not need a number, just like single-dimension arrays, but the subsequent dimensions does. An n x 3 array is located in the memory in such a sequence: 0, 0 0, 1 0, 2 1, 0 1, 1 1, If the compiler knows the number of columns which is 3, it will put the fist element 0, 0 of first row on the first memory location, the first element on second row on the fourth memory location, the first element on third row on the 7th location, Without the number of columns the compiler is not able to organize memory for the array.
A pointer with a value of 0 points to nowhere. If a pointer is a constant pointer, it should be initialized when declared, and it can not be pointed to any other variable. Because of this, a pointer can be used in the called function to receive the array. Then by moving the pointer e. If the size of the variable to which the pointer is pointing to is 4, then actually the value of the pointer will be increased by 3 x 4. Any type of pointer can be assigned to a pointer to void without casting.
However, it can not be conversed. The result may show which one is pointer to a highernumbered element. Pointer arithmetic including increment and difference is meaningless unless performed on one array, because we are only sure that array elements are located one after another. We can not assume two separate variables are put together in the memory.
The following four expressions is doing the same thing: cout cout cout cout 5. When a pointer is pointed to an array or a string, it is actually pointed to the first element of the array subscription 0.
This element can also be represented by ptr[3]. If you point a pointer to the middle of an array, what will happen? The pointer can be used as the name of a new array, whose first element is the element to which the pointer is pointing to. Notice that the number of bytes for a certain type is different for different systems. Just like an array name is the address of the first array element, a function name is a actually the starting address of the function code. A function pointer holds the address of a function, just like a float pointer holds the address of a float variable.
A function pointer can point to either a global function or a class function. My name is Jessy! My name is John! When you want your program to be applicable to different use cases, you may find that at a certian point in your program, you need to invoke a function which has the same signature but different implementation for different use cases. Different client who uses your program may have different implementations. In this case, you have to provide a mechanism so that the client may register his own version of that function to your program before the invoking point, so that your program knows which one to call.
There are three ways to achieve call-back. The OO approach of callback is to let the client class inherit from and implement an interface. In your code you simply hold an interface pointer and call the interface methods through that pointer.
The client program will create his implementation object, assign its pointer to the interface pointer in your class before the calling pointer in your class is reached. However, if the client class is already finished and did not implement the interface you want, you have to use a less OO approach. The client programmer or your do it for him should write a separate matching class for the client class, which inherit from the desired interface with the function you will call back, which provides the service you need by manipulating client-class objects.
In your code you have a pointer to the interface and invoke the service provided by the separate class. The least OO approach is to use function pointers like the above example.
The user is prompted to select an option from a menu e. Each option is severed by a different function. Pointers to different functions is stored in an array of function pointers. It is extremely flexible and therefore can generate every kind of errors if misused. For example, you can only cast an object of a sub-class to its super-class. No other casting between user-defined classes is allowed. However, pointers to different classes can be cast to each other without any restrict.
What is passed in the casting is only the address. So you can cast a pointer to an integer to a Employee-class pointer. Then the Employee pointer will just assume that starting from the passed address it can find all attributes of Employee class. From now on we will talk more about OO issues. As a class, it combined the data attributes and the behavior attributes of an object together, and formed an object which can simulate both aspects of a real-world object.
To distinguish independent functions such as those string handling functions in "string. The "public:" and "private:" labels are called "member access specifiers". All data members and methods declared by the "public" specifier are accessible from outside, and all declared by "private" are only accessible for methods.
Actually an object contains only the data members. Methods do not belong to any specific object. The belong to the class. All objects share one copy of methods. It may improve the performance, but it is not good for information hiding, because the client of the object is able to "see" the implementation of its methods. If a method is defined outside the class body, you have to use keyword "inline" if you want it to be inlined. Add Comment. Save my name, email, and website in this browser for the next time I comment.
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